Low cost RFID systems, typically including an interrogator or “reader” and an electronic label or “tag,” are desirable in a variety of applications, such as retail, supply chain management, logistics, library management, anti-counterfeiting, access control, and baggage claim systems, as just a few examples. Other emerging applications include vehicle toll tracking and/or management. One advantage of RFID systems over conventional barcode and magnetic media-based systems is that RFID systems can be configured to read multiple electronic labels simultaneously. Such a multi-tag capability can enable faster automated data capture and identification, leading to faster and more efficient inventory tracking, sorting, and handling operations, for example.
Referring now to FIG. 1, a block diagram showing a conventional RFID tag system for a single tag application is indicated by the general reference character 100. Computer 102 can connect to interrogation source or reader 104, which can then communicate to tag 110 via antenna 106. Tag 110 can provide information wirelessly to antenna 106 that can then be captured by detector 108 and fed back into computer 102. Tag 110 can, for example, provide a simple bit string of data back to computer 102. For example, in a retail application, tag 110 can convey to computer 102 whether a particular item has been purchased or not.
In expanding typical RFID systems to support multi-tag read capability, anti-collision blocks and/or algorithms can be employed with the interrogator and electronic label or tag device. Two common anti-collision schemes are “tags-talk-first” (TTF) and “reader-talks-first” (RTF). In a TTF approach, the electronic label can reply intermittently as long as it is within a sustained electromagnetic field of the interrogator. This field must be maintained for a period of time greater than a time interval between the intermittently repeated label replies. In an RTF scheme, the interrogator and an electronic label to be read must set up a communication link whereby the electronic label can decode and transmit based on commands and arbitration schemes from the interrogator.
Referring now to FIG. 2, a diagram showing a conventional tag system application for reading multiple tags simultaneously is indicated by the general reference character 200. Toll station 206 can employ a tag system to determine whether cars passing through have arranged for payment (e.g., via a debit or a credit account) to access a road, as an alternative to each car stopping in order to pay a person in a booth at the toll station. Each car passing through may have an associated tag attached to the vehicle (e.g., tags 202-0, 202-1, and 202-2). An applied electromagnetic field can include RF waves 208 to pass information between interrogator/reader (or source/detector) 204 and each of tags 202-0, 202-1, and 202-2. Other such multi-tag read applications include retail, library or inventory management, security, and animal (e.g., pet) identification, for example.
Customization of RFID tags at the integrated circuit (IC) level to embed unique identifiers and/or response characteristics is of high value for retail item level applications (e.g., inventory control, cashier check out, anti-counterfeiting, etc.) or applications with relatively low demands for anti-collision (e.g., library checkout, transit ticket management, etc.). For example, one type of embedded unique identifier is a bar code. An example of embedded unique response characteristics may be found in certain “tags-talk-first” (TTF) anti-collision schemes (see, e.g., U.S. Provisional Patent Appl. No. 60/748,973 [IDR0641], filed on Dec. 7, 2005, and U.S. patent application Ser. No. 11/544,366 [IDR0642], filed on Oct. 6, 2006, the relevant portions of which are incorporated herein by reference, which disclose a technique for embedding unique time delays in tag broadcasts). There are several conventional approaches to incorporating customization by encoding bits in memory, such as those utilizing read-only memory (ROM), one-time programmable (OTP) fuses, and electrically-erasable programmable ROM (EEPROM) elements.
In making ROM elements, the unique ID information may be conventionally encoded in the lithography masks. The cost of mask implementation may be proportional to the number of mask sets required, which can be proportional to the number of unique patterns desired. However, for RFID applications, the relatively large number of unique IDs needed makes mask encoding for this type of customization prohibitively expensive.
OTP fuses offer a high degree of customization, but are limited by the programming requirements. For example, laser programming by blowing select fuses may be limited by the applied laser power, which depends on the line width of the fuse. For thin film transistor (TFT) designs with line widths larger than 2 μm, the power required may be so high that the throughput of conventional laser fuse tools may not be cost effective for RFID devices. Similarly, the limited power available in certain RF applications may restrict the ability to blow select fuses by passing a high current through them.
EEPROM elements are relatively easy to program, but conventional EEPROM elements may have manufacturing process challenges and/or costs that make them a less-than-optimal solution for RFID applications.
An alternative approach to customization utilizes maskless patterning techniques, as they offer high degrees of customization and can be quickly adapted to various applications by changing software parameters. Examples of maskless patterning techniques include laser patterning and inkjetting, using metal nanoparticle- and/or liquid silane-based inks (see, e.g., Kovio U.S. Provisional Pat. Appl. No. 60/697,599 [filed Jul. 8, 2005] and U.S. patent application Ser. Nos. 11/249,167, 11/246,014, 11/243,460, 11/203,563, 11/104,375, 11/084,448, 10/956,714, 10/950,373, 10/949,013, 10/885,283, 10/789,317, 10/749,876, and/or 10/722,255, respectively filed on Oct. 11, 2005, Oct. 6, 2005, Oct. 3, 2005, Aug. 11, 2005, Apr. 11, 2005, Mar. 18, 2005, Oct. 1, 2004, Sep. 24, 2004, Sep. 24, 2004, Jul. 6, 2004, Feb. 27, 2004, Dec. 31, 2003 and Nov. 24, 2003).
However, for certain high performance applications, laser patterning may be preferable to inkjetting because current laser patterning technology can offer higher patterning resolutions. What is needed, however, is a laser patterning process suitable for high performance RFID implementations.